Harvest aids efficacy applied by unmanned aerial vehicles on cotton crop

Chemical harvest aids applied by ground-based machines with heavy wheels and high-volume spraying in cotton (Gossypium hirsutum L.) fields to defoliate leaves and ripen bolls before harvest threaten soil health and result in cotton yield loss. For example, ground-based machines roll over cotton plants at corners and pull the cotton branches between rows, resulting in yield loss. Furthermore, heavy wheels can cause soil compaction, resulting in decreased soil biodiversity. High-volume spraying often results in harvest aids polluting the soil. A new harvest-aid application method that can save water, increase harvest-aid utilization rate without damage to soils and crops is needed to apply chemical harvest aids before harvest. Small plant protection unmanned aerial vehicles (UAVs) with low-volume spraying methods have emerged as pesticide application technologies in recent years in China due to their high efficiency, high flexibility, low labor requirements, water savings and lack of damage to crops and soils. Here, UAVs are developed for chemical harvest-aid application by evaluating the cotton defoliation efficacy, boll opening rate, lint cotton yield and fiber quality components at two cotton field experimental sites in Xinjiang Uygur Autonomous Region of China in 2016 and 2017. Ground-based machine treatment is used as a reference. The assessment is proceeded with the following steps: (1) The spray volume of UAV is optimized in 2016; (2) The experiment of 2016 is repeated to determine the optimal spray volume in 2017. The results show the following: (1) The harvest-aid performance is sensitive to the spray volume in the UAV low-volume spraying treatment, and optimal defoliation efficacy is achieved when the spray volume is 22.5 L/ha and flight velocity is 4 m/s, according to the field tests in 2016 and 2017. (2) Low-volume spraying using UAV has no negative influence on the lint cotton yield and fiber quality components. In conclusion, it is feasible to use plant protection UAV for cotton harvest-aid applications in preparation for machine harvesting.